From e65e4c88748f2d245aa683116a2c6de907186751 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sergey=20M=E2=80=A4?= <dstftw@gmail.com>
Date: Sat, 2 May 2015 23:06:01 +0600
Subject: [PATCH] [utils] Improve prepend_extension

Now `ext` is appended to filename if real extension != expected extension.
---
 youtube_dl/utils.py | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/youtube_dl/utils.py b/youtube_dl/utils.py
index f07679c764..b3abfbc11b 100644
--- a/youtube_dl/utils.py
+++ b/youtube_dl/utils.py
@@ -1349,9 +1349,12 @@ def parse_duration(s):
     return res
 
 
-def prepend_extension(filename, ext):
+def prepend_extension(filename, ext, expected_real_ext=None):
     name, real_ext = os.path.splitext(filename)
-    return '{0}.{1}{2}'.format(name, ext, real_ext)
+    return (
+        '{0}.{1}{2}'.format(name, ext, real_ext)
+        if not expected_real_ext or real_ext[1:] == expected_real_ext
+        else '{0}.{1}'.format(filename, ext))
 
 
 def check_executable(exe, args=[]):